This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/DE00/01550 which has an International filing date of May 15, 2000, which designated the United States of America, the entire contents of which are hereby incorporated by reference.
The invention generally relates to a turbomachine. In particular, it relates to a gas turbine, preferably one including a sealing system for a rotor which extends along an axis of rotation. Even more preferably, the rotor includes a first rotor blade and a second rotor blade which adjoins the first rotor blade in the circumferential direction of the rotor.
Rotatable rotor blades of turbomachines, for example of turbines or compressors, are secured in various designs over the entire circumference of the circumferential face of a rotor shaft which is formed, for example, by a rotor disk. A rotor blade usually has a main blade, a blade platform and a blade root with a securing structure which is fitted to the circumferential face of the rotor shaft in a suitably complementary recess, which is produced, for example, as a circumferential groove or an axial groove, so that the rotor blade is fixed in this way.
For design reasons, after the rotor blades have been inserted into the rotor shaft, gaps are formed by the regions which adjoin one another, and in operation of a turbine these gaps give rise to leaking flows of coolant or of a hot action fluid which drives the rotor. Such gaps occur, for example, between two adjacent blade platforms of rotor blades which adjoin one another in the circumferential direction and between the circumferential face of the rotor shaft and a blade platform which radially adjoins the circumferential face. To limit the possible leaking flows, such as for example the escape of coolant, e.g. of cooling air, into the flow channel of a gas turbine, intensive searches are being made for suitable sealing concepts which are able to withstand the temperatures which occur and the mechanical load caused by the considerable centrifugal forces acting on the rotating system.
DE 198 10 567 A1 has disclosed a sealing plate for a rotor blade of a gas turbine. If cooling air which is fed to the rotor blade escapes into the flow channel, this leads, inter alia, to a reduction in the efficiency of the gas turbine. The sealing plate, which is inserted into a gap between the blade platforms of adjacent rotor blades, is intended to prevent the leaking flows caused by the escape of cooling air. The sealing is produced not only by said sealing plate but also by various sealing pins which are likewise fitted between the blade platforms of two adjacent rotor blades. A multiplicity of sealing elements are required in order to achieve the desired sealing action preventing cooling air from escaping from the adjacent blade platforms.
U.S. Pat. No. 5,599,170 has described a sealing concept for a rotor blade of a gas turbine. A substantially radially extending gap and a substantially axially extending gap are formed by two rotor blades which adjoin one another and are attached to the circumferential face of a rotor disk which can rotate about an axis. A sealing element seals the radial gap and, at the same time, the axial gap. For this purpose, the sealing element is inserted into a cavity which is formed by the blade platforms of the rotor blades. The sealing element has a first sealing face and a second sealing face which respectively adjoin the axial gap and the radial gap.
Moreover, the sealing element has a thrust face which extends obliquely with respect to the radial direction. The thrust face directly adjoins a reaction face which is formed as a partial area of a moveable reaction element arranged in the cavity. The sealing action is produced by the centrifugal forces acting on the moveable reaction element as a result of the rotation of the rotor disk. The reaction element transmits to the inclined thrust face a force, the radially directed component of which acts on the sealing element, so that the first sealing face seals the axial gap, while the axially oriented component of the force on the sealing element leads to the second sealing face sealing the radial gap. This sealing concept is unable to prevent cooling air from escaping into the flow passage of the gas turbine along the circumferential face of the rotor disk through gaps which are formed between the circumferential face of the rotor disk and a blade platform of a rotor blade which radially adjoins the circumferential face.
Similarly complex arrangements with one or more sealing elements, as are described in DE 198 10 567 A1 or U.S. Pat. No. 5,599,170, are also used in a turbomachine to prevent a flowing, hot action fluid, e.g. a hot gas or vapor, from entering gap regions and spaces in a rotor. Penetrating action fluid of this type could lead to considerable damage to the rotor blade. To reduce this risk, generally a plurality of sealing elements are inserted into the blade platform on that side of the blade platform of the rotor blade which faces the flow of action fluid.
EP 0 761 930 A1 and GB 905,582 each describe a turbomachine with a turbine rotor. The turbine rotor is in this case of disk design and is composed of individual rotor disks which are arranged axially adjacent to one another. Rotor blades, which are each secured by means of their blade root in an axial groove in the rotor disk, e.g. an axial fir-tree groove or a hammerhead groove, are arranged on the circumference of the rotor disks. Axial fixing of the rotor blades in the blade root/groove region is effected by securing plates which are mounted in a fixed position on the end sides of the rotor disks. The end-side securing plates can also be used to achieve a certain sealing action with respect to possible penetration of action fluid, for example, a hot gas, in the blade root/groove region. However, the securing plates serve primarily to fix the rotor blades in the axial direction.
GB-A-2 280 478 has disclosed a gas-turbine rotor which has sealing arrangements. In one configuration, the sealing arrangement has sealing points which are arranged on the rotor surface and bear in a sealed manner against a radially inwardly arranged sealing face of a turbine guide vane.
U.S. Pat. No. 4,878,811 has disclosed a rotor blade arrangement of an axial compressor. The rotor blade arrangement is produced by a rotor disk with circumferential groove, a multiplicity of compressor rotor blades being secured in the groove over the entire circumference of the rotor disk, so that a ring of rotor blades is formed. Furthermore, a sealing ring is arranged in a sealing groove over the entire circumference of the rotor disk, resulting in a substantially sealed connection between the rotor disk and the platform of the rotor blade.
The invention is based on an object of providing a highly efficient sealing system for a turbomachine, preferably one including a rotor which extends along an axis of rotation and has a first rotor blade and a second rotor blade which adjoins the first rotor blade in the circumferential direction of the rotor. The sealing system is in particular intended to actively limit the possible leaking flows through gap regions and spaces of the rotor and to be able to withstand the thermal and mechanical loads which occur. In addition, the sealing system is preferably to be designed in such a way that it can be produced as easily as possible and can be employed for various rotors.
According to the invention, an object is achieved by a turbomachine, preferably a gas turbine, including a rotor which extends along an axis of rotation, comprising a circumferential face, which is defined by the outer radial boundary surface of the rotor, and a receiving structure, as well as a first rotor blade and a second rotor blade, which each have a blade root and a blade platform which adjoins the blade root, the blade root of the first rotor blade and the blade root of the second rotor blade being inserted into the receiving structure, so that the blade platform of the first rotor blade and the blade platform of the second rotor blade adjoin one another, and a space is formed between the blade platforms and the circumferential face, in which turbomachine a sealing system is provided on the circumferential face in the space, the sealing system having at least one labyrinth sealing system and a circumferential-face central region, which is bordered in the axial direction by a first circumferential-face edge and a second circumferential-face edge, which lies opposite the first circumferential-face edge along the axis of rotation, being formed on the circumferential face, and in that the sealing system having the labyrinth sealing system is arranged at least partially on the circumferential-face edge.
The invention is based on the consideration that when a turbomachine is operating, the rotor is exposed to a flowing hot action fluid. As a result of the expansion, the hot action fluid applies work to the rotor blades and sets them in rotation about the axis of rotation. Therefore, the rotor with the rotor blades is subject to very high thermal and mechanical loads, in particular on account of the centrifugal forces which occur as a result of the rotation.
A coolant, e.g. cooling air, which is usually fed to the rotor through suitable coolant feeds, is used to cool the rotor and in particular the rotor blades. In this case, leaking flows of both coolant and hot action fluidxe2x80x94what are known as gap lossesxe2x80x94may occur in the space. A space is in this case formed by the circumferential face, which in this case is defined by the outer radial boundary surface of the rotor and by the platform, arranged radially outside the circumferential face, of rotor blades which are arranged next to one another in the circumferential direction of the rotor.
These leaking flows have a very disadvantageous effect on the cooling efficiency and the mechanical installation strength (quiet running and creep rupture strength) of the rotor blades in the receiving structure of the circumferential face. In this context, leaking flows which are oriented along the axis of rotation (axial leaking flows), for example along the circumferential face, are of particular importance. Furthermore, leaking flows perpendicular to the axis of rotation (radial leaking flows), which are directed along a radial direction and therefore substantially perpendicular to the circumferential face, should also be borne in mind.
The invention demonstrates a new way of effectively sealing a rotor with a first rotor blade and with a second rotor blade which adjoins the first rotor blade in the circumferential direction of the rotor in a turbomachine with respect to possible leaking flows. The arrangement takes account of both axial and radial leaking flows. This is achieved by the fact that the sealing system having a labyrinth sealing system is arranged in the space on the circumferential face of the rotor, which face is defined by the radially outer boundary surface of the rotor. As a result of the configuration described, the sealing system seals the space which is formed between the blade platforms and the circumferential face. The space extends in the radial and axial and circumferential directions of the rotor.
In this case, the axial extent of the gap is generally dominant, while its extent in the circumferential direction is greater than the radial dimension. The precise geometry of the space is determined by the specific configuration of the mutually adjacent blade platforms and of the circumferential face. The design of the sealing system described, which has a labyrinth sealing system, can be individually adapted to the particular geometry and requirements with regard to the leaking flows which are to be restricted, the provision of a labyrinth sealing system being particularly effective for sealing the space.
The action of a labyrinth sealing system is based on the most effective possible restriction of the hot action fluid and/or of the coolant in the sealing system and a resulting substantial prevention of an axially directed leaking flow (leak mass flow) through the space. In this case, a residual leaking flow through existing sealing gaps, as generally occur with labyrinth gap seals, for example, can be calculated taking account of the so-called bridging factor. With the same flow parameters upstream and downstream of the seal and identical principal dimensions of the labyrinth sealing system (sealing gap diameter, sealing gap width, overall axial length of the seal), labyrinth gap sealing systems, which are also referred to as look-through seals, compared to so-called tongue-and-groove sealing systems have a leaking flow through the sealing gap which is up to 3.5 times greater. However, on account of the sealing gap which remains, labyrinth gap sealing systems have the considerable advantage over the tongue-and-groove sealing systems that they themselves are suitable for considerable thermally and/or mechanically induced relative expansions in the rotor.
A significant advantage over conventional sealing concepts results from the labyrinth sealing system being arranged on the circumferential face. As a result, it is possible for the labyrinth sealing system to directly adjoin the circumferential face, so that a sealing action is produced. This is particularly suitable for preventing leaking flows in the axial direction along the circumferential face. By way of example, even the penetration of a hot action fluid, e.g. the hot gas in a gas turbine, into the space is substantially prevented and an axially directed flow in the space along the circumferential face is considerably reduced. This protects the material of the rotor, in particular the material of the blade platforms, from the high temperatures and the possible oxidizing and corrosive influences of the hot action fluid. In the radial direction the sealing system having the labyrinth sealing system may be dimensioned in such a way that it directly adjoins the adjacent blade platforms and a sealing action is achieved. In this way, axial leaking flow is virtually completely prevented, or at least is significantly suppressed.
Temperature gradients in the region of the rotor blade attachment area are avoided by preventing leaking flows of hot action fluid and/or of coolant in the space by means of the sealing system. This is where the labyrinth sealing system provides its sealing function particularly efficiently. As a result, any thermal stresses resulting from impeded thermal expansion of rotor components which adjoin one another in the event of temperature differences are reduced. The blade root of a rotor blade and the receiving structure of the rotor which receives the rotor blade and fixes it can therefore be produced with significantly lower tolerances. A lower tolerance has an advantageous effect on the mechanical installation stability of the rotor blade and the quiet running of the rotor. In particular, form fits which are provided for the purpose of securing the blade root in the receiving structure can be provided with a lower clearance, which also correspondingly reduces possible leaking flows through the form fit.
A further advantage is the ease of producing and installing the sealing system. Since the sealing system having the labyrinth sealing system is provided on the circumferential face, it is not necessarily fixedly coupled to a rotor blade. Installation or repair work on a rotor blade, such as for example, exchanging a rotor blade, can therefore be carried out without great difficulty. The sealing system remains unaffected by this work and can therefore be used a number of times.
In a preferred configuration of the turbomachine, the rotor has a rotor disk, which comprises the circumferential face and the receiving structure, the circumferential face having a first circumferential-face edge and a second circumferential-face edge, which lies opposite the first circumferential-face edge along the axis of rotation, the receiving structure having a first rotor-disk groove and a second rotor-disk groove, which is at a distance from the first rotor-disk groove in the circumferential direction of the rotor disk, and the blade root of the first rotor blade being inserted into the first rotor-disk groove and the blade root of the second rotor blade being inserted into the second rotor-disk groove.
Therefore, the securing of the rotatable rotor blade is such that, when the turbomachine is operating, it is able to absorb the blade stresses caused by flow and centrifugal forces and by blade vibrations with a high degree of reliability and to transmit the forces which arise to the rotor disk and ultimately to the entire rotor. The rotor blade can be secured, by way of example, by axial grooves, each rotor blade being clamped individually in a dedicated rotor-disk groove which extends substantially in the axial direction. For low loads, e.g. in the case of axial compressor rotor blades of compressors, simple ways of securing the rotor blade, for example using a dovetail or Laval root, are possible. For steam-turbine end stages with long rotor blades and correspondingly high blade centrifugal forces, as well as the so-called plug-in root, the axial fir-tree root is also suitable. The axial fir-tree securing is preferably also employed for rotor blades which are subject to high thermal stresses in gas turbines.
In the preferred configuration described above, the circumferential face has a first circumferential-face edge and a second circumferential-face edge as partial regions. Based on the direction of flow of a flowing hot action fluid, in particular of the hot gas in a gas turbine, in this case, by way of example, the first circumferential-face edge is arranged upstream and the second circumferential-face edge is arranged downstream. Depending on the particular design details and requirements with regard to the sealing action to be achieved, this geometric division allows a configuration and arrangement of the sealing system over various partial regions of the circumferential face.
The sealing system is preferably arranged on the first circumferential-face edge and/or on the second circumferential-face edge. The labyrinth sealing system may be arranged at least partially on the first and/or second circumferential-face edge. Arranging the sealing system on the first, for example upstream, circumferential-face edge primarily limits the penetration of flowing hot action fluid into the space and therefore prevents damage to the rotor blade. Arranging the sealing system on the second, downstream circumferential-face edge serves predominantly to prevent the escape of coolant, for example cooling air which is under a certain pressure in the space, in the axial direction along the circumferential face over the second circumferential-face edge into the flow passage. Since the hot action fluid expands in the direction of flow, the pressure of the hot action fluid is continuously reduced in the direction of flow. A coolant which is under a certain pressure in the space will therefore escape from the space in the direction of the lower ambient pressure, i.e. at the downstream circumferential-face edge. Arranging the sealing system having the labyrinth sealing system on the first circumferential-face edge and on the second circumferential-face edge closes off the space and accordingly offers highly reliable protection both against the penetration of hot action fluid into the space and the escape of coolant from the space.
Preferably, a circumferential-face central region, which is bordered in the axial direction by the first circumferential-face edge and the second circumferential-face edge, is formed on the circumferential face, the sealing system being arranged at least partially on the circumferential-face central region. In this case, the labyrinth sealing system is preferably arranged on the circumferential-face central region. The circumferential-face central region forms a partial region of the circumferential face. Therefore, there are various options for arranging the sealing system on various partial regions of the circumferential face together with the first and second circumferential-face edges. Depending on design details and requirements with regard to the sealing action to be achieved, it is possible to determine a suitable solution, with the sealing system arranged on various partial regions. Combinations of various partial regions are also conceivable when arranging the sealing system. Therefore, with regard to adapting to specific requirements in terms of the sealing action to be achieved, the sealing system described offers a very high degree of flexibility.
The sealing system having the labyrinth sealing system preferably has a sealing element which extends in the circumferential direction. The space extends substantially in the radial and axial directions and in the circumferential direction of the rotor. A sealing element which extends along the circumferential direction of the rotor in the space is particularly suitable for preventing the possibility of axial leaking flows of coolant and/or also of hot action fluid with a high degree of efficiency. For example, an axial leaking flow in the upstream direction, for example a hot gas leaking out of the flow passage of a gas turbine, which spreads out along the circumferential face is effectively prevented by the sealing element. In this case, the leaking flow is delayed by the obstacle in the space and ultimately comes to a standstill on that side of the sealing element which faces the leaking flow (simple restrictor). That side of the sealing element which is remote from the leaking flow and that part of the space which adjoins it in the axial direction are already effectively protected from being exposed to the leaking medium, e.g. hot action fluid or coolant, by the simple sealing element. The way in which the sealing element operates can therefore be similar to the way in which the labyrinth sealing system operates, and this enhances the sealing action.
A considerable improvement to the simple solution described above with a sealing element extending in the circumferential direction results from combining the sealing element with one or more further sealing elements. In a preferred configuration, at least one further sealing element is provided, which extends in the circumferential direction and is arranged at an axial distance from the sealing element. This multiple arrangement of sealing elements considerably reduces possible leaking flows in the space. In particular, it is possible, for example, for the sealing element to be arranged on the first circumferential-face edge and for the further sealing element to be arranged on the second circumferential-face edge. As a result, the space is sealed both upstream and downstream with respect to axial leaking flows. The space is in particular protected very effectively against the possibility of the penetration of hot action fluid both from the upstream region at higher pressure and from the downstream region at lower pressure in the flow passage. At the same time, the sealed space can be used effectively by a coolant, e.g. cooling air. The coolant is fed to the space under pressure and is used primarily for efficient internal cooling of the highly thermally stressed rotor, the blade platform and the main blade which radially adjoins the blade platform.
A further advantageous use for the pressurized coolant in the space includes in utilizing its barrier action with respect to the hot action fluid in the flow passage. The design of the sealing elements and the selection of the pressure of the coolant in the space mean that the pressure difference between the coolant and the hot action fluid is adequately low yet sufficiently high to achieve a barrier action with respect to the hot action fluid. For this purpose, the pressure of the coolant which prevails in the space must be only slightly above the upstream pressure of the hot action fluid. The greater the sealing action of the sealing elements, the smaller any residual leaking flows of coolant into the flow passage become.
At least the labyrinth sealing system is preferably produced integrally in the sealing system, in particular by removing material from the rotor disk. If the sealing system is designed, for example, as a single labyrinth sealing system, it is produced just by means of at least two sealing elements on the circumferential surface, which extend in the circumferential direction of the rotor disk and are at an axial distance from one another. These sealing elements may be formed by metal restrictor plates which are turned out of the solid. The integral production method has the advantage that there is no need for an additional joining element between the labyrinth sealing system and the circumferential face. Therefore, in terms of process engineering, the rotor disk can be machined and the labyrinth sealing system produced in a single step carried out on a lathe, which is very inexpensive. Furthermore, thermally induced stresses between the rotor disk and the labyrinth sealing system do not play any role, since only one material is used. Alternative configurations of the sealing element, for example by means of a metal restrictor plate welded onto the rotor disk or by means of a metal restrictor plate which is jammed into a groove into the circumferential face, are also possible.
On its outer radial end, the sealing element preferably has a sealing point, in particular a knife edge. Residual leaking flows through the space are decisively influenced by the sealing gap width which can be achieved, i.e. for example the distance between the outer radial end of the sealing element and the adjoining blade platform which is to be sealed. To make the sealing gap width as small as possible, it is provided for the outer radial end of the sealing element to be sharpened. In this case, it is possible, in particular to bridge the sealing gap, by producing the sealing point or the knife edge with a small dimension compared to the radial installation dimension of the blade platform. By drawing the sealing tip or the knife edge onto the blade platform, the sealing gap is bridged when the rotor blade is inserted into the receiving structure, for example into an axial groove in a rotor disk. In this way, the sealing gap is closed off, an improved seal is achieved and the axial leaking flow is further reduced. Compared to conventional designs, therefore, it is also possible to considerably reduce the installation dimension of a rotor blade in the receiving structure. The minimum installation dimension which has hitherto been customary of between approximately 0.3 and 0.6 mm can be reduced to approximately 0.1 to 0.2 mm by means of the new design, i.e. is reduced by approximately two thirds.
The labyrinth sealing system preferably comprises the sealing element and/or the further sealing element. The sealing element and the further sealing element are therefore part of the labyrinth sealing system. The labyrinth sealing system is preferably designed as a labyrinth gap sealing system. In a preferred configuration, a gap sealing element is provided for sealing a substantially axially extending gap, the gap being formed between the blade platform of the first rotor blade and the blade platform of the second rotor blade and being in flow communication with the space. The gap sealing element prevents a leaking flow through the gap. A leaking flow of this type is substantially radially directed and may be oriented both radially outward from the space through the gap and radially inward through the gap into the space.
In this case, various designs are possible: For example, if the flow passage of the turbomachine, e.g. of a compressor or a gas turbine, adjoins the gap in the radially outward direction, the gap sealing element prevents the penetration of the action fluid, e.g. of the hot gas in a gas turbine, radially inward into the space through the gap. As a result, the rotor, in particular the rotor blade, is protected from oxidizing and/or corrosive attack in the space. At the same time the gap sealing element prevents coolant, e.g. cooling air, from escaping from the space through the gap radially outward into the flow passage. In an alternative configuration, a cavity may also adjoin the gap on the radially outer side, this cavity being formed by the first and second rotor blades which adjoin one another in the circumferential direction (known as the box design of a rotor blade). In this case, the gap sealing element firstly prevents the possibility of hot action fluid penetrating from the space through the gap radially outward into the cavity. Secondly, the cavity which is sealed by the gap sealing element can be acted on by a coolant, e.g. cooling air. This coolant is under pressure in the cavity and is available, for example, for efficient internal cooling of the rotor blade which is subject to high thermal loads or for other cooling purposes. A further advantageous use of the pressurized coolant in the cavity consists in utilizing its barrier action with respect to the hot action fluid in the flow passage.
The gap sealing element is preferably produced by a metal gap sealing plate which has a gap-sealing edge which engages in the gap under the action of centrifugal force and closes off the gap. Designing the gap sealing element as a metal gap sealing plate represents a simple and inexpensive solution. In this case, for example, a design as a thin metal strip which has a longitudinal axis and a transverse axis is possible. In this case, the gap-sealing edge extends substantially centrally on the metal strip along the longitudinal axis and can be produced in a simple way by bending over the metal strip. The gap sealing element is expediently arranged in the space. When the turbomachine is operating, the gap sealing element is then, as a result of the rotation, pressed firmly by the radially outwardly directed centrifugal force against the mutually adjoining blade platform, the gap-sealing edge engaging in the gap and effectively sealing the latter.
The gap sealing element is preferably made from a highly heat-resistant material, in particular from a nickel-base or cobalt-base alloy. Moreover, these alloys also have sufficient elastic deformation properties. The material of the gap sealing element is selected to match the material of the rotor, with the result that contamination or diffusion damage is avoided. Furthermore, uniform thermal expansion or contraction of the rotor, in particular of the blade platform of the rotor blade, is ensured.
The gap sealing element preferably radially adjoins the sealing system. The combination of the gap sealing element with a sealing system arranged on the circumferential face, in particular with a labyrinth sealing system, results in particularly effective sealing of the space against the possibility of leaking flows of hot action fluid and/or of coolant. In particular, as a result a centrifugally assisted sealing action of the gap sealing element is retained in order to seal an axially extending gap. In this combination, the sealing system reduces the substantially axially oriented leaking flows, while the gap sealing element reduces the substantially radially directed leaking flows. Furthermore, this separation of functions readily allows flexible design adjustment to different rotor geometries. Consequently, the gap sealing element and the sealing system complement one another very effectively.
In a further preferred configuration, the sealing element engages in a recess, in particular in a groove, in the circumferential face. In this variant, the sealing element is not necessarily a part of the labyrinth system, but it is part of the sealing system. The sealing element is prevented from falling out and/or from being thrown out under the action of centrifugal forces in steady-state operation or in the event of a transient load on the turbomachine is achieved by the fact that the sealing element engages in a suitable recess. Furthermore, the recess produces a sealing surface, which is expediently designed as a partial area of the recess, on the circumferential face. In the case of a groove, this sealing surface is formed, for example, at the base of the groove. To achieve the optimum sealing action when the sealing element is active, the sealing surface is produced with a suitably low and well-defined surface roughness. After the actual production of the groove, for example by abrading material from the circumferential face by means of a milling or turning operation, a sealing surface with the desired roughness can be produced on the base of the groove by polishing.
The sealing element is preferably moveable in the radial direction. This has the effect of causing the sealing element to move away from the axis of rotation of the rotor in the radial direction under the action of centrifugal force. This property is deliberately exploited in order to achieve a significantly improved sealing action at the blade platform of a rotor blade. Under the action of centrifugal force, the sealing element comes into contact with the blade platforms which are at a radial distance from the circumferential face and adjoin one another in the circumferential direction and is pressed firmly onto the blade platforms. The radial mobility of the sealing element can be ensured by suitable dimensioning of the recess and of the sealing element. Furthermore, it is advantageous that, as a result, the sealing element can be removed and, if appropriate, exchanged without problems for any maintenance to be carried out or in the event of failure of the rotor blade without using additional tools and without the risk of the sealing element becoming stuck as a result of oxidizing or corrosive attack under high operating temperatures. Furthermore, a certain tolerance of the sealing element which engages in the recess, in particular in the groove, is very useful, since as a result thermal expansion is permitted, and therefore thermally induced stresses are avoided in the rotor.
The sealing element preferably comprises a first partial sealing element and a second partial sealing element, the first partial sealing element and the second partial sealing element engaging in one another. The partial sealing elements may be designed in such a way that they provide, in a particular manner, a partial sealing function for different regions in the space which are to be sealed. These different regions in the space are formed, for example, by suitable sealing surfaces at the base of the groove, on the blade platform of the first rotor blade or on the blade platform of the second rotor blade. As a result of being arranged as a pair of partial sealing elements, the partial sealing elements combine to form one sealing element, the sealing action of the pair being greater than that of a single partial sealing element. By suitably adapting the design of the partial sealing elements to the partial regions in the space which are to be sealed, it is possible for the sealing action of the paired partial sealing elements to be greater than that which can be achieved, for example, with a single-piece sealing element.
Preferably, the first partial sealing element and the second partial sealing element can move in the circumferential direction relative to one another. This provides a matched system comprising partial sealing elements. The relative movement of the partial sealing elements in the circumferential direction allows matched engagement of the partial sealing elements in one another as a function of the thermal and/or mechanical loads acting on the rotor. The matched system of partial sealing elements may be designed in such a way that under the action of the external forces, such as for example the centrifugal force and the normal and bearing forces, it to a certain extent adjusts itself in order to provide its sealing action. Furthermore, possible thermally or mechanically induced stresses are compensated for significantly more successfully by the movable pair of partial sealing elements.
In a preferred configuration, the first partial sealing element and the second partial sealing element each have a disk-sealing edge, which adjoins the circumferential face, and a platform-sealing edge, which adjoins the blade platform. In this case, the platform-sealing edge may in each case be further functionally divided into partial platform-sealing edges. By way of example, for a partial sealing element there may be a first partial platform-sealing edge and a second partial platform-sealing edge, the first partial platform-sealing edge being adjacent to the blade platform of the first rotor blade and the second partial platform-sealing edge being adjacent to the blade platform of the second rotor blade. This functional division makes it easy to adapt the design of the partial sealing elements to the particular installation geometry of the first and second rotor blades in the receiving structure. Suitable designing of the partial sealing element ensures that the disk-sealing edge is sealed against the circumferential face and the platform-sealing edge is sealed against the blade platform of the rotor blade, producing the best possible form fit.
The paired arrangement of the first and second partial sealing elements to form a sealing element provides a particularly effective seal. The first and second partial sealing elements preferably overlap one another, with the platform-sealing edge and the disk-sealing edge of the first partial sealing element being adjacent to the platform-sealing edge and diskt-sealing edge, respectively, of the second partial sealing element. As a result, the paired arrangement of the two partial sealing elements produces a good positive lock, and consequently the sealing element produces a good seal against the penetration of hot action fluid into the space and/or the escape of coolant into the flow passage.
The sealing element is preferably made from a highly heat-resistant material, in particular from a nickel-base or cobalt-base alloy. These alloys also have sufficient elastic deformation properties. The result is that the material of the sealing element, in order to avoid contamination or diffusion damage and to ensure a uniform thermal expansion of the rotor, in particular of the blade platform of the rotor blade, is selected to match the material of the rotor.
In a preferred configuration, in the turbomachine with the rotor extending along an axis of rotation, the receiving structure is produced by a circumferential groove, the circumferential face having a first circumferential face and a second circumferential face which lies opposite the first circumferential face along the axis of rotation, these faces in each case axially adjoining the circumferential groove, the sealing system being provided in the space on the first and/or second circumferential face.
When the turbomachine is operating, the means of securing the rotor blades must with great reliability absorb the blade stresses caused by flow and centrifugal forces and by the vibrations of the blade and must transmit the forces which are generated to the rotor disk and ultimately to the entire rotor. In addition to securing the rotor blade in an axial groove, an arrangement in which the rotor blade is secured in a circumferential groove is also in widespread use, particularly for low and medium stresses. In this case, various configurations are known depending on the stress (c.f. I. Kosmorowski and G. Schramm, xe2x80x9cTurbo Maschinenxe2x80x9d [Turbomachines], ISBN 3-7785-1642-6, published by Dr. Alfred Hxc3xcthig Verlag, Heidelberg, 1989, pp. 113-117). By way of example, for short rotor blades with low centrifugal forces and bending moments, the so-called hammerhead connection method, which is easy to produce, is used. In the case of longer rotor blades and therefore higher blade centrifugal forces, in the case of rotors of disk design, particular design measures have to be used to prevent the rotor disk from bending in the region of the first and second circumferential faces at the level of the circumferential groove. This can be achieved, for example, with the aid of a rotor disk which is of solid design at the level of the circumferential groove, a hooked hammerhead root or a hooked sliding root. However, a more efficient transmission of forces to the rotor disk is achieved, for example, by the circumferential fir-tree securing means. In any event, the described concept for sealing the space can be transferred very flexibly to a rotor in which the rotor blade is secured in a circumferential groove.
The turbomachine is preferably a gas turbine.